DQt: Qt bindings using extern(C++)

[MGW]

Can you explain in more detail some points that are difficult for 
me:

widgets/label.d file. I see a C++ mapping of class QLabelPrivate 
to structure D
extern(C++, class) struct QLabelPrivate;
this makes sense.

I see below an implementation of a class D named QLabel
class /+ Q_WIDGETS_EXPORT +/ QLabel : QFrame
in which I see calls to methods of the QLabel class.

I don't understand at what stage (where exactly) the mapping
QLabelPrivate structure methods onto QLabel methods.

I expected to see something like:
QLabelPrivate dd = QLabelPrivate(...);
and then
dd.MetodsQLabel(...)

Can you explain this place in more detail.